I just assumed it was ethanol - I see them used a lot under chafing dishes. I did a little googling and all I found was:

"Sterno is one of the most prominent brand name creators of gel fuel and, according to the company's website, cooking directly over the flame is perfectly safe in terms of chemical emissions. They do, however, caution against open flame cooking because drippings that can come from food cause flare-ups that can result in injury. You should also not eat food that has cooking fuel on it or that has fallen in the flame."

You can eat it, it's just terrible for you and you'll end up hammered. People used to eat/drink Sterno to get drunk in the 1920s, when it was better known as "Canned Heat." The rock band "Canned Heat" is named for a blues song written around that era by Tommy Johnson, who wrote it about his addiction to Sterno.